Overview of the process flow of electroplating raw material bright sulfate electroplating tin

Overview of the process flow of electroplating raw material bright sulfate electroplating tin

Bright sulfate tin plating current efficiency is high, deposition speed is fast, can work at room temperature, and the raw material is easy to buy, the cost is low, at the same time the tin coating is soft, small pores, can be used for surface decoration coating such as silver, but also for solderable coating.Therefore, bright sulfate tin plating is widely used in the electronic and light industries.

However, there are some problems in the process, such as the easy oxidation of divalent tin and the decomposition of additives, which lead to the turbidity of the plating solution, the deterioration of the properties and the narrowing of the bright area of the coating, so it is necessary to improve it.

2. Bath composition and process flow

2.1 function of each component in the bath

The main components of bright sulfate tin-plating solution are stannous sulfate and sulfuric acid.

2.1.1 function of main components in bath

2.1.1.1 stannous sulfate

Stannous sulfate is the main salt, and the content is generally controlled at 40 ~ 100g/L.However, the results of production experiments show that although high concentration of stannous sulfate can increase the cathode current density and accelerate the deposition rate, the dispersion ability of the plating solution is obviously decreased, and the coating crystallization is coarse and the bright area is smaller, and the treatment period of the plating solution is even greatly shortened.

It is advisable to control the content of SnSO4 within 20 ~ 60g/L. If the lower limit is set, "compensation" can be carried out by accelerating the circulating speed of the bath and the moving speed of the electrode (cathode or anode), etc., and excellent products can still be plated, but it should not be too low.

2.1.1.2 sulfuric acid

Sulfuric acid can reduce the activity of stannous ions, prevent their hydrolysis, improve the conductivity of bath and anode current efficiency.When the amount of sulfuric acid is insufficient, the stannous ion is easy to oxidize to tetravalent tin.

From the point of view of dynamics, when there is enough H2SO4, the hydrolysis of bivalent tin can be slowed down and the plating solution can be stabilized. In actual production, the content of H2SO4 is generally between 80 and 150mL/L.

2.1.2 additives

Tin-plating brightener is generally made up of main brightener, auxiliary brightener and carrier brightener.Electroplating materials

2.1.2.1 main light agent

Acid bright tin plating brightener phyletic and various, sums up can be divided into two broad categories: category 1 is mainly aromatic aldehyde, aromatic ketone, esters and unsaturated organic acid derivatives, 2 class mainly west Buddha base class (the basic structural unit - CH = N - CH = CH - or - CH = CH - CH = N -), composed of acetaldehyde condensation with adjacent methyl propyl amine, acid bright tin plating is effective whitening agent, can be used alone, also can be used with the first class l brightener, when used with category 1 brightener, significantly broaden the light area, effectively eliminate coating white mist.

The bright action of organic brighteners is mainly reflected in the adsorption on the cathode, which is too strong or too weak to obtain the ideal bright coating.Because adsorption is too strong, desorption potential is too negative, serious hydrogen evolution, easy to form pinhole;When the adsorption is too weak, the desorption potential is relatively positive, the coating crystallization is rough.Only proper adsorption can achieve a good luminous effect.

Therefore, when preparing the combined brightener, the additives with too strong, appropriate and too weak adsorption should be used in an organic way, so as to achieve the goal of moderate adsorption and a wide range of adsorption potential, and the amount of each combination is determined by the experiment.At present, benzylidene acetone, cuminic aldehyde, diphenylketone, O - chlorobenzaldehyde and so on are used as main photoagents, among which benzylidene acetone is commonly used.